Astronauts Tackle Delicate Hubble Telescope Maintenance

An STS-125 crewmember onboard the space shuttle Atlantis snapped a still photo of the Hubble Space Telescope following grapple of the giant observatory by the shuttle's Canadian-built remote manipulator system on May 13, 2009 during NASA's last mission to the telescope.Credit: NASA.

HOUSTON - Two astronauts in bulky
spacesuits will open up the Hubble Space Telescope on Friday in a delicate
tune-up to keep the aging observatory pointed straight.

Atlantis spacewalkers Michael Massimino
and Michael Good are slated to float outside their shuttle to replace some of Hubble?s
batteries and all six of its gyroscopes, which are used to accurately point
the telescope at cosmic targets. Giving Hubble new gyroscopes is the mission?s
number one task, mission managers said.

The job sounds mundane, but without
the new parts Hubble won?t be able to reliably maintain its position in space
precisely enough to observe
the universe or conserve the power generated by its solar wings, mission
managers said.

Today?s spacewalk is the second of
five consecutive excursions by the crew of Atlantis during
NASA?s fifth and final mission to overhaul Hubble. On Thursday, a different
team of spacewalkers installed a
new camera and docking gear on Hubble, and also replaced a malfunctioning computer
unit that beams images and data back to Earth.

Vital service call

While Hubble has six gyroscopes,
only three are working and the telescope has been operating in a two-gyroscope
mode for years in order to keep the last one as a spare. Today?s spacewalk will
reset Hubble back to full capacity and should help extend
its mission life another five years, Burch said.

But it is a far from simple task. To
do the job, Massimino will have to squeeze inside a Hubble access door with
barely enough room to move and his feet rooted to a foot restraint. He can use
his hands to install the new gyroscopes, but could seriously damage fragile
nearby sensors if his spacesuit rubs against anything at all, mission managers
said.

?We?re in a really delicate place
inside the telescope,? Good told SPACE.com before flight. ?So I?m going to breathe a
big sigh of relief when we get everything done and close those doors. And even
the doors are tricky.?

Good will be perched at
the tip of Atlantis? robotic arm for most of the spacewalk in order to move the
new parts from the shuttle?s payload to Hubble.

Astronauts have had trouble closing
the gyroscope access doors on Hubble in past
spacewalks. Massimino and Good have spent hours just practicing to open and
close them, mission managers said.

Hubble?s batteries, which have not
been changed since the telescope launched in 1990, are also showing signs of
age.

?Just like any other battery, the
battery in your car, batteries run down over time,? said Keith Walyus,
Hubble mission operations manager at NASA?s Goddard Space Flight Center in Greenbelt,
Md. ?So we?re going to install a new set of batteries, which will give us an
extended life of Hubble.?

Three of Hubble?s six batteries will
be replaced in today?s spacewalk. The rest are expected to follow in a Monday
excursion.

Extra inspection

Astronauts will also use Atlantis?
robotic arm to scan about 40 heat-resistant tiles for dings on the left side of
the shuttle?s nose. The tiles were accidentally skipped during a heat shield
inspection earlier this week, though NASA has given Atlantis a clean bill
of health with respect to launch debris.

NASA has kept a close eye on shuttle
heat shield integrity since launch debris led to the loss of the shuttle
Columbia and its seven-astronaut crew in 2003. Atlantis and Hubble are flying
in a 350-mile (563-km) orbit that is littered with space junk. The astronauts
will perform a standard second inspection of their shuttle?s heat shield next
week after leaving Hubble and NASA has the Endeavour orbiter standing by to fly
a rescue mission in the unlikely event Atlantis suffers serious damage from
space debris.

Late Thursday, the astronauts said
they were looking forward to today?s spacewalk. They?ll also have an easy way
to separate the two spacewalkers to avoid confusion over their same first
names.

Massimino goes by the nickname ?Mass?
and has been providing mission updates as @Astro_Mike on
the microblogging
Web site Twitter. Good, an Air Force colonel, goes by the call sign ?Bueno,?
which is simply his last name translated in Spanish.

?I think the Mike and Mike show will
be fun, they?ve got the [gyroscopes] down to a science,? Atlantis skipper Scott
Altman radioed down to Mission Control late Thursday.

SPACE.com is providing continuous
coverage of NASA's last mission to the Hubble Space Telescope with senior
editor Tariq Malik in Houston and reporter Clara Moskowitz in New York. Click here for mission
updates, live spacewalk coverage and SPACE.com's live NASA TV video
feed.